Telephone installation



April I, 1941. M. HEBEL, 2.237,073

TELEPHONE INSTALLATION Filed June 5, 1937 f/V VENTR //artz'fz A/ebel TUBA/EKS.

Patented Apr. 1, 1941 UNITED stres grant trace mamie I rnnnrnonn iNs'rALLA'rioN Martin Rebel, Hechendorf-on-the-Pilsensee, Oberbayern, Germany Application June 5, 1937, Serial No. 146,654 In Germany June 5, 1936 15 Claims. (Cl. PiS- 18) It is usual for the signals which in telephone installations indicate to the calling subscriber the condition of the desired line, to be transmitted back from that selector stage up to which the connection has been made. Thus, the socalled "selecting or "dialling signal which indicates to the subscriber that he has been connected to a free numerical current impulse receiver and can begin emitting selecting current impulses is usually transmitted from the calling subscriber's feed circuit. The *'busy signals which are transmitted when all outlets from a selector are busy are evolved in the selector which is unable to find a free outlet. The "ringing signal which indicates that the desired Subscriber's line is idle is transmitted from the final selector. An arrangement has already been proposed with which, if the called subscriber is engaged, the connecting devices are automatically released up to the first group selector; it has also been proposed to use an intercepting circuit and to extend the release as far as the calling subscriber's individual relays. In these cases, the '*busy signal would be transmitted from the first group selector or the subscriber's individual relays. The ringing signal would also be transmitted always from the final selector.

The object of the invention is to simplify the transmission of these signals. With this end in view, in accordance with the invention, the devices provided for giving the various signals are arranged in the calling subscriber's exchange and are Controlled from the distant exchanges. With this arrangement, the signal transmitting devices are preferably associated with the calling f subscriberys feed circuit. By uniting all the signal transmission devices at one and the same place, it can be arranged that the calling subscriber always receives the signals at the same rhythm and the same pitch. These signals, moreover, will not be excessively weakened or damped. A particularly marked improvement is thus effected in cases in which connections are made through a number of exchanges connected by lengthy lines. It is usual for the ringing" signals transmitted by the last selector stage of the terminal exchange to be transmitted to the calling subscriber over a lengthy line so that they are frequently received in a very weakened state. In telephone installations in which amplifiers are used, the amplifiers have been used for strengthening the signals. This, however, requires the use of special balancing devices because the amplifiers when connected to a line which has not yet been connected through to the desired subscriber readily tend to oscillate. All these special devices can be avoided in accordance with the inventicn as the speech amplifier only has to be connected after the called subscriber has replied, that is to say, after the connection has been made to the desired line.

One embodiment of the invention is shown in the accompanying 'drawing in which:

Figure 1 shows diagrammatically the crcuits of a call finder and a group selector.

Figure 2 shows the circuits of an inductively coupled line and the transmitters associated therewith, and

Figure 3 shows the circuit of a final selector.

It will first of all be assumed that the group selector shown in Figure 1 is directly connected to the nal selector shown in Figure 3 and that the line shown in Figure 2 has not yet been connected.

When the subscriber TN lifts` his reoeiver, a multi-step" relay T is energised through its Winding I in the first stage. The contacts tl and tz are thus closed and a call finder AS is thus brought into operation. When the call finder nds a free outlet, the relay C responds (wind.- ing I), the relay T (winding II) is energised in the second stage and opens the calling Circuit at the contacts t3 and tli. By means of its contacts cl and C2 the relay C connects the speech lines so that the windings I of the feed circuit relays A and B are energised. The calling subscriber now receives the "dialling signal which is transmitted through the contact glc (closed in the normal position of the group selector) to the windings II of the relays A and B from a signal transmitter connected to the terminal si. The numerical current impulses transmitted by the subscriber are received in the usual manner by the relay A and are used forfisetting the group selector. A slow-to-release relay V is energised through the contact al during each train of current impulses and releases at the end of each train. When the group selector finds a free line to a final selector, the relay P responds and by means of its contacts pl and 122 connects through the speech lines. The relay 4G in the final selector (Fig. 3) is thus energized. The current impulses are transmitted by means of a contact 11,2 through one speech wire to the final selector and are received there by the relay which in known manner sets the final selector. The slow-to-release relay 11V is -kept enerby. the contact 4a during each train of current impulss and releases at the end of leach train. During the second setting movernent of the final selector the wiper shaft of the selector mechanically closes a contact wk so that a circuit is prepared for a relay IIR. A relay IIU is energised from the beginning of the energisation of the final selector. When the relay 'IV drops at the end of the second train of current impulses acting on the final selector, the circuit for the testing relay 4P and also the circuit for the relay 4B are closed. The relay 4B, responds, opens the circuit for the sloW-to-release relay 4U at its contact 41' so that the relay 4U releases and v itself opens the circuit for the testing relay 4P at its contact lIu. The delay in release of the relay 4U thus limits the testing time If the called subscriber's line is busy, the relay IIP cannot respond during the testing time. On

release of the relay 4U, the b-wire of the speechv line is connected through the resistance WI -to the negative side of the source of current.V In the' group selector (Figure 1) therelays Fr and Mare connected to the b-wire of the speech line. The relay F1' is non-Sensitive and can only respond to a strong current, while the relay M is Sensitive enough to respond to weak currents. The resistance WI is so great that the current which flows `over the b-wire of the speech line is so weak that only the relay M is actuated, The contact mi connects up the "busy signal transmitter connected to the terminal 82 and the "busy" signal is transmitted inductively to the calling sub- 'scriber over the windings II of the relays A and B. If it is desired that in the case of the desired line being engaged, the connection should be'released up to the calling subscribefis individual relays, the relay M is provided with a further contact m2 whichA short circuits the winding II of the relay C' and thus causes the relay C to release. When the relay C releases, the circuit for the winding II of the subscriberls relay T is also interrupted. The subscriber's individual relays include a relay R, the winding I of which was energized through the contact t5 after the testing by the call finder so that the relay reverses its contacts. If now the energising circuit of the relay T is opened, this relay first restores the contacts actuated in the second stage into the normal position. When the contacts 153 and td close, a circuit is closed through the winding I of the relay T and the winding II of the relay R. In this circuit, the relay T is held energlsed in the first stage and the relay R is also held energised. The "busy signal transmitter is now connected to the winding IlI of the relay T by the contacts 13 and tI and the signal is transmtted inductively to the calling subscriber. The relays remain energised until the subscriber replaces his receiver. The group selector is restored into the normal position in the known manner on release of the relay C.

If the line seized by the final selector is free, the relay 4P responds on closing of the testing circuit. The b-wire 'of the speech line is connected over the contacts 4u3 and 4104 and the resistance W2 to the negative side of the source of current for the duration of the delay in release of the relay 4U, The resistance W2 is considerably smaller than the resistance WI. Owing to the considerably Stronger fiow of current through the b-wire of the speech line in the group selector, both the relay M and the relay Fr (Winding I) are energised. 'The relay Fr responds by means of its contact rl, closes' a holding current through its winding II and by reversing its contact r2 makes the busy signal transmitter connected to the terminal 82 inoperative. At the same time, the

"free" signal transmitter connected to the terminal 83 is connected up. The contact r3 con- .nects the winding I of a two-step relay Z to the bwire of the speech line. 'This relay, however, cannot respond because it is short circuited over the resistance-WZ of the final selector.

The delay in the release of the relay lU is approximately 100 milliseconds. When the relay 'SU drops, the connection of the resistance W2 with the b-wire of the speech line is broken at the contact 4u3. The short circuit for the winding I of the relay Z is thus removed and the relay Z is energised in the first stage through the relays M- and Fr and reverses its contacts el I, zl, and zl3. The contact eII connects one end of the winding I of the relay Z preparatorily to the positive side of the source of current. The contact zI2 closes a holding current through the winding II of the relay Z while the contact .2I3 makes the "free signal transmitter connected to the terminal 83 inoperative, and in its place connects up the periodic '*free signal transmitterconnected to the terminal 84. If the line is free, the subscriber therefore receives first a short "free signal for the duration of the delay in response of the relay lIU of the final selector and then a periodic free signal corre'sponding to the periodic call transmitted to the desired subscriber in the final selector. This periodic "free signal transmitter may be connected in known manner to the periodic call device of the exchange in question.

The transmission of the periodic call in the final selector is not shown in the circuit, When the desired subscriber replies, the relay 4Y responds and by means of the contact y, connects the b- Wire of the speech line to'the negative side of the source of current over the resistance W2. As the winding I of the relay Z is now connected to the positive side by the contact II, the relay Z is energised in the second stage by the current flowing over the b-wire. The contact zsI now cuts out the relay M and the winding I of the relay Dr. The contact 282 closes a holding current through the winding I I of the relay Z. The contact e83 also disconnects the winding I of the relay Z from the speech line and the contact e84 interrupts the periodic "free signal. At the same time, the contact .285 prepares the metering which is carried out in the known manner when the calling subscriber replaces his receiver and the relay C in consequence releases.

As may be seen, all signals are thus given from the calling subscriber's feed circuit. For the busy signal, a weak flow of current through the b-wire of the speech line is used and for the "fi'ee signal, a short strong fiow of current is used w which, at the beginning, switches in the "fi'ee s signal transmitter and at the end switches over to a periodic 'free signal transmitter. When the called subscriber replies, the "free signal is switched off by a second strong fiow of current through the b-wire of the speech line, and the metering operation is put into operation.

If a ubusy signal is to be given should a group selector not find a free line, it is only necessary to connect the b-wire in the selector stage in question to the negative side of the source of current over a .great resistance. In the group selector shown, the relay M can be locally energised through a second winding on a contact closed by the selector running over its contact bank. 4

If the connection is made through inductively coupled trunk lines, the operation performed for the signal transmission must result in the transaesvzova mission of alternating current impulses through the trunk line. An arrangement of this kind is shown in Figure 2. The outgoing transmitter UI is seized by the group selector of Figure 1 so that the relay 2C responds. The relay 2A is energised through the contacts 2c2 and 2u for the duration of the delay in response of the relay 2V and through its contacts al and 20.2 transmits an alternating current impulse. This impulse is received in the incoming transmitter U2 by a relay 3A which energises the seizing relay 30. The latter holds itself energised and with its contact 302 energises the relay 4G of the final selector. The current impulses which 'are sent out by the subscriber and transmitted by the relay A of the group selector (Figure 1) are converted by the relay 2A of the transmitter UI into alternating current impulses and transmitted by the relay 3A of the transmitter U2 through the o-wire of the speech line as direct current impulses. If the desired subscriber's line is busy, the b-Wire is connected in the final selector (Figure 3) to the negative side of the source of current over the resistance Wi and 'a sensitive relay 3M responds in the incorning transmitter U2. The relay K however does not respond to the weak current. By means of its contact 3ml, the relay SM energises the relay 35 and the latter, with its contacts 38| and 382, sends back alternating current through the trunk line. The lcircui-t of the relay ISv passes through the contact 3m of the relay 3N which has been preparatorily energised from the beginning of the seizing of the' incoming transmitter. This relay 3N is short circuited by the contact 31722 so that the energisation of the relay 33 and the transmission of the alternating current is limited to the duration of the delay in release of the relay SN. The alternating current is received in the outgoing transmitter by the relay 2W which, with its contact Zw causes energisation of a relay Y and at the same time short circuits the relay ZN which has been energised from the beginning of the seizing of the outgoing transmitter. The delay in release of the relay 2N is shorter`than that of the relay 3N which determines the duration of the alternating current transmission. The relay 2N thus drops during the received long altern'ating current impulse. At the end of the alternating current impulse the relay X in addition to the relay Y is energised over its winding I on release of the relay 2W. The contact :cl now connects the b-wire of the speech line to the negative side of the source of current over the contact 277. and the resistance Wii. The resistance W'3, just like the resistance W! of the final selector, is of such dimensicns that the. weak current fiowing over the b-wire can only energise the relay M of the group selector. The relay M of the group selector then switches in the "busy signal transmitter in the manner already described and causes the connection to be released.

If the desired subscriber is free, then the b-Wire of the speech line is connected to the negative side of the source of current over the resistance WE for the delay in release of the relay QU. The strong current which is thus caused to flow through the b-wire energises both the relay 3M and the relay K (Winding I). The relay K, by

means of its contact kl, 'closes the Circuit for the` relay 38 and 'at the same time by means of its contact 762 energises a relay L which, by means of its contact ZI, re-opens the circuit for the relay 3S. The relay L is slow-to-attract so that the relay 35 is energised for the duration of the vdelay in attraction 'and sends back alternating current through the trunk line. By reversal of the contact Icl, the contactiiml of the relay 3M is made inoperative. The contact kB of the relay K maint'ains the connection between the winding I of the relay K and the b-wire of the speech line after the response of the relay L so that the relay K does not drop until the fiow of current through the b-wire ceases. By means of its contact kl, the relay K for the duration of the delay in the response of the relay L again closes a circuit for the relay ES which for the second time transmits a short alternating current impulse. On response of the relay K, a two-step relay O (winding I) is energised in the first stage over the ,contact M and by means of its contact oi prepares the energising circuit for its Winding II. 'When the relay K releases, this circuit is closed so that the relay O responds in the second stage, closes a holding circuit for itself by means of its contact 03 and, by means of its contact 02, prepares the energisation of the relay T. The temporary strong flow of current through the b-wire thus causes the transmission of two alternating current inipulses through the trun'r: line.

At the outgoing transmitter, the relay Y is energized at the beginning of the first altern-ating current impulse and, by means of its contact y, prepares 'the Circuit for the winding I of the relay X. At the end of the first current impulse, the relay X is energised in additicn to the relay Y. The contact :nl is thus 'closed and the b-wire is now connected to lthe negative side of the source of current over the resistance Wii (the relay ZN has not released owing to the shor'tness of the 'alternating current impulse received). The resistance Wt, just like the resistance "W of the final selector LW, is so dimensioned 'that a strong current iiows over the b-wire. Consequently, the relay Fr in the group selector is energised and switches in the "fi'ee signal transmitter in the manner already described.

At the beginning of the second alternating current inipulse, the energising Circuit for the relay Y is interrupted but the relay X is kept energised by Way of its winding II. It is not until at the end of the second alternating current impulse that the relay X also drops and interrupts the flow of current through the b-wire of the speech line. On termination of the fiow of direct current through the b--wire of the speech line, in the inanner already ciescribed, the relay Z in the group selector is energised in the first stage by way of its winding I and switches in the pei'iodic "free signal transmitter (terminal S4;) instead of the irc-e signal.

If, now, when the subscriber repies, the relay QY of the final selector is energised and the contact fly causes the b-wire of the speech line to be connected to the ncgative side of the source of current over the resistance W 2, the relay K in the incoining transmitter U2 responds and seizes the relay L so that the relay ZiS is energised for the duration of the delay in attraction of the relay L and transmits aiternating current to the' trunk line. At the same time, the relay T is energised by the contact kt and by means of its contact t removes the short cii'cut for the relay BN so that this relay is positively prevented from releasing.

The short aiternating current inipulse which is sent back over `the trunl': line again first causes the relay Y to be energised and then the relay X o-f the outgoing transmitter UI. The contact xl again connects the resistance Wii to the`b-wire of the speech line s'o that a strong direct current fiows over the'b'-wire which, in the manner already described, energises the relay Z of the group selector in the second stage. The contact 284 disconnects the nfree signal transmitter and the contact 285 starts the metering procedure.

The weak direct current fiowing through the b-wire of the speech line which is transmitted when the "busy" signal is given is thus converted at the incoming transmitter into a long alternating current impulse which is in turn converted in the outgoing transmitter to a weak direct current. The first strong direct current fiow which is transmitted from the final selector when the indication is given that the desired subscriberls line is idle is converted into two shortl alternating current impulses which are reconverted in the outgoing transmitter into a strong direct current fiowng for a limited time. The second strong direct current impulse which is transmitted when the desired subscriber removes his receiver is reconverted in the incoming transmitter into a short alternating current impulse which in turn is converted back in the outgoing transmitter into a strong direct current. This conversion into alternating current impulses which are transmitted through the inductively coupled trunk lines can naturally be repeated a number of times at various points in a connection if a number of trunk lines are seized. If amplifiers are provided for the amplification of the speech current, they are not seized until the subscriber replies and thus actuates the switch means associated with the transmitters, for example, the relay T in the incoming transmitter U2 so that the amplifiers are only brought in when the speech line has been completely connected.

I claim:

1. A multi-exchange automatic telephone system in which audible signals are automatically transmitted to a calling subscriber to indicate to him whether the line to which he desires to be connected is idle or busy comprising means at the called exchange for transmitting back to the calling exchange diiferent signals according as the desired line is idle or busy, means at the calling exchange for transmitting the desired audible sign'als to the calling subscriber, means at the calling exchange for bringing said last-mentioned transmitting means into operation on receipt of said signals from the called exchange and meansv at the calling exchange actuated on receipt from the called exchange o-f a signal indicating that the desired line is busy for releasing the connection made by the calling subscriber.

2. A multi-exchange automatic telephone system in which audible signals are automatically transmitted to a calling subscriber to indic'ate to him whether the line to which he desires to be connected is idle or busy comprising means at the called exchange for transmitting back to the calling exchange a relatively weak current over one of the wires of the speech line when the desired line is busy and a relatively strong current of predetermined length over the same Wire when the desired line is idle, means at the calling exchange responsive to said relatively Vweak current for transmitting the desired audible busy signal to the calling subscriber, and means at the calling exchange responsive to said relatively strong current for transmitting the desired audible idle signal to the calling subscriber.

3. A multi-exchange automatic telephone system as claimed in claim 2, in which said lastmentioned means comprise means for transmittinga continuous audible signal to the calling subscriber during the fiow of said relatively strong current and means for transmitting an intermittent audible signal when. said flow ceases.

4. A multi-exchange automatic telephone system as claimed in claim 2 in which said lastmentioned means comprise means for transmitting a continuous audible signal to the calling subscriber during the fiow of said relatively strong current and means for transmitting an intermittent audible signal when said fiow ceases and comprising means at the called exchange arranged, when the called subscriber hangs up, to transmit a relatively strong current over said Wire of the speech line and means at the calling exchange responsive to said last-mentioned current for interrupting the 'transmission of the audible idle signal.

5. A multi-exchange automatic telephone system in which audible signals are automatically transmitted to a calling subscriber .to indicate to him whether the line to which he desires to be connected is idle or busy comprising a plurality of exchanges connected by trunk lines having an inductive transformer at each end, means at the called exchange for transmitting back a relatively weak current over one of the wires of the speech line when the desired line is busy and a relatively strong current over the said wire when the desired linev is idle, means associated with the transformer at the called exchange responsive to said weak and strong currents for converting them into alternating current impulses of diiferent length, means associated with the transformer at the calling exchange responsive to said alternating current impulses for converting them back to weak and strong currents and transmitting them over the Wire of the speech line at the calling exchange corresponding to the wire of the speech line at the called exchange over which said first-mentioned 'weak and 'strong currents were transmitted and means at the calling exchange lresponsive to said last-mentioned weak and strong currents for transmitting the desired audible signals to the calling subscriber.

6.1n a telephone system, an automatic exchange, a plur'ality of subscribers' lines terminating at said exchange, automatic switches in said exchange dilferently operated according as a called'subscribefs line is busy or idle, a further automatic exchange, a plurality of subscribers' lines |terminating at said exchange, means associated to said further exchange Vfor .transmitting different audible signals to a calling subscriber's line terminating at said exchange, a trunk line connecting said exchanges and means in said further exchange Controlled b-y 'said automatic switches over said trunk line for bringing into operation said signal transmitting means 'according as said called subscriber's line is busy or idle.

'7. In a telephone system, an automatic exchange, a plurality of subscriber's lines terminating at said exchange, automatic switches in said exchange differently operated according 'as a called subscriber's line is busy or idle, a further automatic exchange, a plurality of subscriber's lines terminating at said exchange, a trunk line conneclting said exchanges, and means in said further exchange controlled by said automatic switches over said trunk line for -transmitting a busy tone or a ringing tone over a calling subscriber's line according as said called subscriber's line is busy or idle.

8. In 'a telephone system at least one calling subscriber's line, at least one feed Circuit connected to said line, at least one connector, at least one called subscriber's line seizable by said connector, automatic selectors for connecting said feed Circuit to said connector, switch means associated With said connector and differently operated according as said calling subscriber's line is busy or idle, and means associated With said feed Circuit and Controlled by said switch means for transmitting a ringing tone over said calling subscribens line if said called subscriber's line is free.

9. In a telephone system a called connector, at least one calling subscriberis line seizable by said connector, 'automatic switches associated with said connector and differently operated according as said subscriber's line is busy or idle, means for transmitting ringing current to said called subscriber's line controlled by said automatic switches, a feed Circuit, at least one calling subscriber's line connected to said feed Circuit, 'at least one selectcr connecting said feed circuit to said connector, and means associa-ted With said feed Circuit and controlled by said automatic switches for transmitting an intermittent signal current over said calling subscriberis line if said call-ed subscriberis line is free.

10. In a telephone system, an automatic exchange having a plurality of ccnnectors, a plurality of subscribers' lines terminating at said exchange and connected to the fixed contacts of said connectors, automatic switches diiferently operated according as a desired subscriber's line is busy or idle, means controlled by said automatic switches for transmitting ringing current over an idle desired subscriber's line, a further automatic exchange, a plurality of subscribens lines temninating at said further exchange, a trunk line connecting said exchanges and means in said further exchange controlled by said autov,

matic switches over said trunk line for transmitting 'a ringing tone over a calling subscriber's line if said desired subscribefs line is idle.

ll. An automatic telephone system comprising a plurality of exchanges, trunk lines connecting y said exchanges, a plurality of subscriber's sets having impulse transmitting devices, a subscriber's line connecting each of said subscribers' sets to one of said exchanges, an impulse vcontrolled connector switch at each of said exchanges, test means associated individually With said connector switches for testing a called subscribefs line, time switching means for making said test means effective during a predetermined time after the setting of said connector switches, means arranged at each of said exchanges for transmitting different audible signals to a calling subscriber connected to the same exchange to indcate whether a called subscriber's line is idle or busy, backward signal transmitting means arranged at each exchange, backward signal receiving means arranged at each exchange for bringing said audible signal transmitting means into operation in accordance with the nature of the received signal, and means associated with said connector switches for controlling the backward signal transmitting means at the same exchange, said last mentioned means being controlled by said test means and by said time switching means for the transmission of a direct current impulse of predetermined length to said backward signal transmitting means when a called subscriber's line is idle.

12. An automatic telephone system comprising a plurality of exchanges having selectors lcontrolled by current impulses, trunk lines Connecting said exchanges, a plurality of subscribers' sets having impulse transmitting devices and connected by subscriber's lines to said exchanges, means associated with a called exchange for transmitting a backward signal when 'a called subscriber's line is idle and a different backward signal when the called subscriber removes his receiver, means associated with a calling exchange for transmitting different -audible signals to the calling subscriber indicating whether 'a called Subscribe-rs line is idle or busy, means at saidl calling exchange for receiving said backward signals and for bringing said audible signal tr'ansmitting means into operation in `accordance with the nature of the received backward signal, .said audible signal transmitting means being 'adaptecl to transrnit on receipt of said first mentioned backward signal first of all a continuous signal and then an intermittent signal.

13. An automatic telephone system according to cl-aim 12, in which said backward signal receiving means are adapted to stop the transmission of said intermitten-t signal on receipt of the backward signal indicating that the called subscriber has removed his receiver.

14. An automatic telephone system, comprising a plurality of exchanges, trunk lines inductively coupled to said exchanges, a plurality o-f subscriber's sets connected by subscriber's lines to said exchanges, -means arranged at a calling exchange for transmitting to the calling subscriber different audible signal currents indicating whether a called subscriber's line is idle o-r busy, means associated with a trunk line and arranged in the called exchange for transmitting back- Ward signals by alternating current impul'ses when the called subscriber's line is idle and also when the called subscriber removes his receiver and backward signal receiving means associated with said trunk line and arranged at the calling exchange and. adapted, on receipt of said back- Ward signal to bring said 'audible signal transmitting means into and out of operation.

15. An automatic telephone system according vto claim 14, comprising also means arranged at the Calling exchange for preparing the metering operation, said means being controlled by said backward signal receiving means on receipt of a backward signal indicating that the called subscriber has removed his receiver.

MARTIN HEBEL. 

